The present invention relates generally to digital imaging systems and, more particularly, to a calibration and setup procedure for determining a separation distance between a source and a digital detector in an imaging system.
The installation and setup procedures for digital imaging systems can be complex and time-consuming. To comply with customer requirements and various regulatory and safety standards, such procedures generally require the determination of a variety of factors, including the accurate positioning of a x-ray source with respect to a x-ray detector. For example, the determination and establishment of fixed setpoints (or detent positions) for setting the separation distance between the x-ray source and x-ray detector and calibrating the system such that an accurate readout of the separation distance can be obtained are typical setup procedures. The determination and establishment of this separation distance, referred to as the source-to-image distance (SID), assists in appropriately controlling the size of the x-ray field during diagnostic use of the imaging system. SID is utilized to control the size of the x-ray beam in relation to the physical size of the x-ray image receptor to minimize the amount of non-diagnostic radiation that a patient may be subject to in the course of a diagnostic procedure. Further, certain regulatory standards specify that the SID must be clearly displayed to the operator or user of the system with a certain level of accuracy.
Generally, known installation and calibration procedures for establishing fixed SED setpoints and corresponding SID readouts require the presence of a field engineer who, through a trial and error process, calibrates the imaging system and installs fixed, preset detent positions that lock the x-ray source into various repeatable separation distances from the detector. For example, the field engineer may install an electromechanical switch, or other device, in the ceiling or the superstructure of the x-ray source that indicates to the user in a tactile or otherwise perceptible manner that the x-ray source is at one of the preset SID positions. Many radiographic imaging systems include industry-standard SID setpoints at separation distances of, for example, 40 inches, 60 inches, and 72 inches.
The installation and calibration procedure, however, becomes even more complex if the detector is non-stationary. In such event, the field engineer may repeat the setup and calibration procedure at multiple detector positions and install several setpoint or detent devices at the corresponding multiple determined SID positions.
Once the preset SID positions are determined and marked with a detent device, the SED positions are fixed. Thus, a user of the imaging system is not afforded flexibility in the event that the user may desire a SID position that is non-standard. Accordingly, even though either the x-ray source or the x-ray detector could be moved to a variety of different positions such that patients of various sizes could be accommodated or various anatomical parts could be more easily imaged, the actual positions in which the x-ray source could be located with respect to the x-ray detector are restricted to only those few positions which have corresponding fixed detent setpoints.
Conventional methods to calculate the source-to-image distance are unreliable and time consuming. These methods always required some parameter to be measured. Generally, operators conduct tests to calculate these parameters, and may encounter operator and calibration errors. Proposed solutions are adequate, however they themselves have certain drawbacks such as inaccurate measurements. These proposed solutions all require some known measured parameter to help guide the operators to calculate the source-to-image distance. Since the measurements supplied may be inaccurate, the data calculated can be unreliable and unsuitable for calibration purposes. Additionally, as mentioned above, the current techniques for calibrating a digital imaging systems are time consuming and error prone.
Thus, it would be desirable to provide a system and method for installing and calibrating a digital radiographic imaging system that would avoid time-consuming iterative procedures for determining fixed SID positions and for providing a calibrated readout and display of the actual SID. It would be further desirable if such a system and method would result in the elimination of, or reduced reliance on, fixed setpoints and physical fixed setpoint devices, thus affording greater flexibility and increasing the reliability of the system.
The present invention addresses one or more of the shortcomings noted above.
The present technique involves calculating the SID by utilizing a known relationship. For instance, the energy delivered from a uniform source to a surface normal to an area is proportional to the area, and inversely proportional to the square of the distance from the source to the surface of the area. Using this relationship, the SID is calculated by determining the intensity generated by two separate exposures. The SID for the two exposures are unknown and may be picked randomly, however the change in the distance from the first SID to the second SID is recorded. The technique provides that once the levels of intensity are measured for the same area, the SID may be calculated using the inverse square law as recited above. In another embodiment, the intensity levels of the generated exposures are held constant and a first and second times are measured with respect to the intensity levels. The measured times are then applied to the relationship governed by the inverse square law to determine the source to image distance.